They are literally enemies in the dungeon. In a pile of dudes clashing on the first floor there are Temple Bannerets who you can attack and one who you cannot. From a strictly gameplay standpoint that is bad design.

Temple Banneret in Sohr Kai? Sure. No problem. Aymeric is there with you. He's brought his dude along to fill out the ranks. Cool. You're fighting a bunch of dragons and magic fans.. no issue there.

Meanwhile Xelphatol has a House Fortemps Banneret. They already exist. And you're in The Vault with Haurchefant. Why wouldn't he bring his dude with him?